It's good that folks working on browsers are working on making this easier, but I don't think you can really rely on this for GET requests.

It's often easier to smuggle a same-origin request than to steal a CSRF token, so you're widening the set of things you're vulnerable to by hoping that this can protect state mutating GETs.

The bugs mentioned in the GitHub issue are some of the sorts of issues that will hit you, but also common things like open redirects turn into a real problem.

Not that state mutating GETs are a common pattern, but it is encoded as a test case in the blog post's web framework.